The present invention relates to a method and a device for guiding a web of material (1) which is guided and transported between rotating rollers.
In the production and the processing of flat webs of material these webs are guided and transported between rotating rollers. In order to transport the web a certain level of tension is produced in the longitudinal direction of the web of material. Due to this tension in the direction of travel, folds or shifts arise in the longitudinal direction which are undesired and which later produce lateral elongations in the reel which may result in the material being completely unusable. Accordingly, it is necessary to smooth and straighten the folds and shifts in the running web of material brought about by the tensile stress in the longitudinal direction by means of tensile forces in the crosswise direction.
Devices for spreading webs of material are known in the state of the art. US 22 89 196 describes what is referred to as the banana roller. This cylindrical roller is composed at least on the surface of an elastomeric material and is specially shaped. The roller is curved over its entire length and is pressed against the running web of material. When the roller is pressed into the running web of material, the shape of the roller causes spreading in the transverse direction. However, the transmission of force by transverse forces that can thus be generated and the transverse movement achievable in this case is extremely small and, therefore, unusable for many applications.
The underlying aim of the present invention is to provide a method and a device for spreading a flat web of material (1) which is guided and transported via rollers. The method is intended to ensure that the web of material (1) can be guided and transported without folds and elongations in the longitudinal and transverse directions. At the same time it is of particular importance that the method can be adapted, i.e. the method should be equally successfully employed at different speeds of travel of the web of material (1) and for different materials. In addition the device should require low maintenance and have little need for repair.
This task is solved by a method for guiding a flat web of material (1) in which the web of material (1) runs in an arrangement of rotating rollers at a web speed vF and the web of material (1) is guided in both peripheral regions via at least one spreader roll (2) which produces a tensile stress in the transverse direction, i.e. crosswise relative to the direction of travel of the web of material (1), wherein this tension in the transverse direction is controlled by closed-loop control of the circumferential speed vR of the spreader roll (2) and/or by open-loop control of the angle and/or the contact surface area (3) between the surface of the roll (5) and the web of material (1) and wherein the circumferential speed of the spreader roll (2) vR is greater than the web speed vF.